At the entrance to fabric tentering frames, it is necessary to properly position the lead-in rails having traveling pin chains carried thereon for engaging the selvage of the fabric and moving the fabric forward along a tentering frame. The lead-in rail members must be accurately positioned in response to the lateral variations in the position of the selvage edge as the fabric is fed onto traveling pins so as to uniformly align and place the selvage on the pins.
Many devices have been heretofore proposed for solving the problem of positioning the lead-in rail at the selvages of the cloth such as shown in U.S. Pat. Nos. 2,673,384, 3,150,431, and 3,216,081. However, such devices provide only limited traction for driving the movable infeed rail member back and forth to uniformly engage the fabric selvage. Since it is often necessary to change the direction of the rail member instantaneously, such devices become incapable of such movement due to wear of the drive apparatus.
When rack and pinion gear arrangements are used, the teeth of the gear members become worn due to the continuous sudden changing of lateral directions resulting in excessive play between the gear members and inaccurate responsive movement of the rail member.